Moulds

ABSTRACT

A reinforced mould, including a mould body having in at least one end surface thereof a mould cavity which presents relatively sharp corners when seen in cross section, and in which the mould body has arranged along at least part of its axial length a pretensioned reinforcing means in the form of at least one winding of thin metallic strip material and is slotted generally axially along at least two of said corners to form separate body portions, said body portions being held in contiguous relationship solely by the pre-tensioning force exerted by the reinforcing means on said body.

llriite States Patent [191 Strandell 1*May'141, 1974- MOULDS [56] References Cited [75] Inventor: Per-Olof Strandell, Taby, Sweden UNITED STATES PATENTS [73] Assigneez Sandvik k i p k 3,365,786 1/1968 Takemura et a1 29/446 Sandviken Sweden 3,608,351 9/1971 Strandell 72/467 2,882,759 4/1959 Altwicker.. 72/467 X Notice; The portion of the term of this 3,461,506 8/1969 Rice et a1 18/34 R patent subsequent to Sept. 28, 198 has n i m Primary Examiner-Milton G. Mehr [22] Filed: Oct. 12, 1972 21 Appl. No.: 296,897 [57] ABSTRACT Y A reinforced mould, including a mould body having in Relted Apphcauon Data at least one end surface thereof a mould cavity which [63] Commuano of June 1970 presents relatively sharp corners whenseen in cross section, and in which the mould body has arranged along at least part of its axial length a pre-tensioned [30] Forelgn Apphcanon Pnomy Data reinforcing means in the form of at least one winding JLll'lC 25, Switzerland of metallic strip material and is lotted generally axially along at least two of said corners to form sepa- U-S- CL rate portions aid portions being in Int. Cli contiguous relationship solely the pre tensioning [5 e d 1'' earch 72/467; 74/446; 18/34 R, force exerted by the reinforcing means on said body.

' 1 Claim, 3 Drawing Figures This is a continuation, of application Ser. No. 47,684, filed June 19, 1970, now abandoned.

The present invention relates to a mould of the type which includes a mould body having in at least one end surface thereof a mould cavity, which when seen in cross section presents at least relatively sharp corners, the mould body being encircled along at least part of its axial length by a pre-tensioned reinforcement comprising at least one winding of metallic, strip material which has a thickness of at most a few tenths of a millimeter, and the whole of the bottom face of each turn of a winding being in abutment with the upper face of the preceding turn of said winding.

When producing articles by, for example, forging or compacting powder in a mould of the type referred to, high tensile forces are liable to occur in the aforementioned corners as a result of elastic deformation occurring when subjecting the mould to loads during use, said forces being liable to result in cracking or chipping of the mould. The primary object of the present invention is to eliminate this disadvantage in moulds of this type, which is achieved by the fact that the mould body is slotted substantially axially along two or more of said corners to form separate body portions and by the fact that the body portions are held pressed together in the slotted regions solely by the pre-tensioning force exerted on the mould body of the reinforcementaFor example, a mould having a mould cavity of generally rectangular cross section can be slotted or-divided along two diagonal corners of said cavity, the body portions being held together at the slotted regions by the pretensioning force provided by the reinforcement, even when the mould is being used, for example in forging or powder compacting operations. The' compressive pretensioning force exerted by the reinforcement must not therefore be completely relieved during the forging or pressing operation when using such moulds.

When using moulds of the type referred to, the surfaces defining the mould cavity are liable to be subjected to high pressure forces. These pressure forces can cause those regions of the mould body presenting relatively large cavity defining surfaces to bulge, especially if these relatively large surfaces are essentially flat, and thereby cause an undesired curvature in said surfaces. In accordance with an advantageous develop-. ment of the invention such bulging of the mentioned mould body regions is prevented by the fact that the radial distance fromthe center axis of the slotted or divided body to its periphery is made greater at the zones most subjected to bending forces, when the tool is i being used, than in the remaining zones of the mould body. In this respect the periphery of 'the mould body at each of said zones most subjected to bending forces is preferably curved with a curvature radius of a length which is smaller than the radial distance from the center axis of the mould body to the periphery of the mould body in the zone in question. In this way, the pre-tensioning forces exerted by the reinforcement will increase towards the center of the loaded region in a manner whereby a pre-tensioning force isobtained along the periphery of the mould body which varies in essentially the same manner as the aforementioned pressure forces.

The invention will now be described with reference to a number of embodiments, shown diagrammatically in the accompanying drawing. FIGS. 1-3 respectively show in cross section in first, a second and a third embodiment of the mould of the invention.

In FIGS. 1-3 the reference numeral 10 identifies a diagrammatically illustrated mould body having a mould cavity 11. The cavity 11, which when viewed in cross section exhibits relatively sharp corners, may be in the form of a blind hole or may extend axially through the whole of the body 10. Arranged around the body 10 is a reinforcement formed by a winding 12 of thin, stretched, metallic strip material. The thickness of the strip material is at a few tenths of a millimeter, although extremely thin bands, e.g., having a thickness of only a few hundredths of a millimeter may be used to advantage. For instance, favorable results have been obtained when reinforcing moulds with high-strength steel bands having a thickness in the region of 0.003 mm. The thickness of the strip material used in the reinforcement of the mould according to the invention suitably lies below 0.4 mm, preferably below 0.2 mm. However, the thickness of the strip material should preferably not be less than 0.01 mm and suitably exceed 0.02 mm. A suitable reinforcing material is for instance steel strip hardened to bainite structure which is endowed with high tensile strength combined with a high degree of toughness, although other material of high tensile strength and preferably also a relatively high degree of toughness can also beused. Holes and other arrangements located on the mould to facilitate the positioning thereof in a mouldingapparatus, such as a foundry or powder compacting press, have been omitted for the sake of clarity.

In accordance with the invention, in order to prevent the formation of cracks and the like at the corners of the mould cavity 11 as a result of excessively high tensile forces, the mould body 10 is slotted or divided axially or generally axially along two or more of said corners to form separate body portions, identified by reference numeral 13in FIG. 1, 14 in FIG. 2 and 15 in FIG. 3. The body portions I3, 14 and 15 are held pressed against each other in the slotted regions or division planes 16 solely by the pre-tension'ing forces exerted on the body 10 by the reinforcement formed by winding 12.

As shown in FIGS. 1 and 2, it may be suitable in the case of a mould cavity which exhibits a rectangular, elongated cross section to divide the body 10 axially along two diagonal corners of the cavity 11, whereas in the case of a cavity of triangular cross section it may be expedient to divide the body axially along all the corners of the cavity, as shown in FIG. 3.

In the embodiment shown in FIG. 1, the body formed by body portions 13 has a circular cross-sectional shape. Other cross-sectional shapes are possible, however. For example, in order to render the body portions more resistant to bending it may be expedient to construct the body 10 in a manner whereby the radial dis tance from the axial center axis of the divided mould body to its periphery is greater in the body zones most subjected to bending loads when the mould is being used, i.e., those zones of the body portions 14 and 15 situated opposite the central area of the cavity sides 17 in FIG. 2 and 18 in FIG. 3, than in the other zones of the mould body; As will also be seen from FIGS. 2 and 3, each of the zones of body portions 14 and 15 most subjected to bending loads preferably exhibit in cross section an arcuate periphery with a curvature radius of a length which is smaller than the radial distance from the center of axis of the body to the periphery of the body in the zone in question.

Although only one winding 12 has been shown in the drawing it should be understood that more than one winding can be used to reinforce the mould body, windings having more turns and/or affording a higher degree of pre-tension may be used in regions of the mould body which are subjected to higher stresses than other regions thereof, as is described in more detail in my co pending Application No. 796,852, filed at Feb. 5, 1969. Furthermore, the width of the winding or the width of at least some of the windings, seen in axial section, may decrease radially outwards from the periphery of the body 10 in such a way that the pre-tensioning force applied to the body through the winding or windings varies along the length of the body essentially proportionally to the forces acting radially and peripherally thereon when the tool is being used. It should also be understood that the illustrated and described embodiments can be modified within the scope of the following claims.

What is claimed is:

l. A mould having in at least one end surface thereof a mould cavity which in cross section presents at least relatively sharp corners and which is separable generally axially along at least two of said corners to form separate mould sections, a pretensioned reinforcement covering at least part of the axial length of the mould and comprising at least one winding or metallic strip material having a thickness of at most 0.4 mm with the whole of the bottom face of each turn of said winding being in abutment with but not secured to the upper face of the preceding turn thereof, the separate mould sections being held pressed together solely by the pressure exerted by said winding strip material, the mould being shaped so that the radial distance from the center axis of the mould to its periphery is greater in the zones of the mould most subjected to bending forces when the mould is being used than in the other zones of the mould, said periphery being arcuate in shape with a radius of curvature of a length which is less than said radial distance. 

1. A mould having in at least one end surface thereof a mould cavity which in cross section presents at least relatively sharp corners and which is separable generally axially along at least two of said corners to form separate mould sections, a pretensioned reinforcement covering at least part of the axial length of the mould and comprising at least one winding or metallic strip material having a thickness of at most 0.4 mm with the whole of the bottom face of each turn of said winding being in abutment with but not secured to the upper face of the preceding turn thereof, the separate mould sections being held pressed together solely by the pressure exerted by said winding strip material, the mould being shaped so that the radial distance from the center axis of the mould to its periphery is greater in the zones of the mould most subjected to bending forces when the mould is being used than in the other zones of the mould, said periphery being arcuate in shape with a radius of curvature of a length which is less than said radial distance. 